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KMID : 0360419780140010001
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Korean Journal of Pharmacology
1978 Volume.14 No. 1 p.1 ~ p.11
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The Calcium Release from Cardiac Mitochondria by Sodium and Potassium
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Abstract
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The Na^(+)-and K^(+)-induced Ca^(++) release was measured isotopically by Milipore filter technique in mitochondria isolated from rabbit ventricles.
The release of Ca^(++) from mitochondria could be induced by 1-3 mM of Na^(+) added in incubating medium under the presence of 0.5mM EGTA to prevent the released Ca^(++) from rebinding with mitochondrial membrane. The amount of Ca^(++) released was increased by increasing the concentration of Na^(+) added.
100mM K^(+), in itself, did not induce the Ca^(++) release from cardiac mitochondria, the Na^(+)-induced Ca^(++) release, however, was potentiated by the presence of K^(+). The potentiation of Na^(+)-induced Ca^(++) release by K^(+) was proportional to the Na^(+)/K^(+) ratio presented in the incubating medium.
Among the monovalent cations other than Na^(+), the release of Ca^(++) from cardiac mitochondria was shared only by Li^(+).
The Na^(+)-induced Ca^(++) release could be also observed in the mitochondria isolated from liver and kidney. However, the Na^(+) sensitivity was somewhat lower in liver and kidney mitochondria than in heart mitochondria. The release of Ca^(++) induced by Na^(+) in the mitochondria isolated from the experimentally produced failured heart was not different from that in the normal heart mitochondria, and was not directly modified by 10^(-6)~10^(-5) M of Ouabain.
From the experiments, it was suggested that the Ca^(++) released from mitochondria by Na^(+) could be used in excitation-contraction coupling process to initiate the contraction of the cardiac myofibrils.
Futhermore, it appeared that the phenomenon of Ca^(++) release from cardiac mitochondria by Na^(+) and K^(+) might be related to the inotropic effect of digitalis glycoside which could bring about the increase of Na^(+) or the reduction of K^(+) intracellulary through the inhitition of Na^(+), K^(+)-ATPase.
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